A low cost wavelength sensor using dual layer photodiode

Wavelength sensing using ultra low cost electronic circuits is a prime demand in numerous industrial systems. This work proposes an approach towards wavelength sensing in fiber optic devices using a dual layer/ dual wavelength photodiode. A dual wavelength photodiode WS-7.56-TO5 manufactured by Pacific Silicon sensor was used for this application. One of the layers of the photodiode has peak responsivity at 550 nm wavelength and the other one has peak responsivity at 880 nm wavelength. Fiber coupling for the photodiode was conducted which houses a lens assembly in order to concentrate the light incident on the effective sensing area of the photodiode. The associated electronic circuitry consists of a logarithmic ratio amplifier with variable gain and a thermal sensor. Temperature compensation for the photodiode was conducted during calibration using the outputs of thermal sensor. The circuit outputs voltage signal which varies almost linearly with varying wavelength. The circuit was tested for its wavelength sensing efficacy both for peak wavelength in case of monochromatic source and mean wavelength for broadband source. Good variation in output voltage was observed during testing the set up using different single and broadband wavelength sources.